i) Field of the Invention
This invention relates to a method and apparatus for removal of diluent water from an aqueous fluid mixture, especially an aqueous organic liquid to increase the concentration of the organic liquid in water.
The invention has particular application in the treatment of diluted spent aircraft deicing fluid to recover the deicing fluid at an acceptable concentration in water.
ii) Description of Prior Art
Ice is removed from the wings of aircraft prior to flight, by spraying the wings with a deicing fluid. Typically this deicing fluid is an aqueous solution of ethylene glycol or propylene glycol or a mixture thereof. This solution typically contains about 55%, by weight, of the glycol and 45%, by weight, of water together with minor amounts of additives such as surfactants and inhibitors.
The deicing fluid, also referred to as aircraft deicing fluid (ADF) is recovered from the tarmac where the aircraft deicing is carried out, and typically is scavenged through gravity drains or by vacuum trucks. The recovered ADF is diluted by aqueous precipitation, for example, snow and ice, which it contacts on the surface of the aircraft or on the tarmac, and is also contaminated with various contaminants including dissolved runway deicing salts, grit, traces of fuel and lubricating oils and other debris.
Traditionally the collected material is sorted according to its approximate concentration of glycol and stored in tanks for subsequent processing.
Different commercial procedures for recovery of the glycol involve filtration, deionization or distillation. Canadian Patent Specification 2,116,827 of A. Viszolay et al describes stripping water away using a packed heated tower and distilling the glycol under vacuum.
Canadian Patent Specification 2,106,358 P. Eastcott et al employs a concentrator having a packing medium of glass shards providing a labyrinth for flow of air in one direction and thin streams of glycol in a generally opposite direction.
Canadian Patent Specification 2,074,031 B. Dobrofsky employs reaction of the water component of diluted spent deicing fluid with an agent such as calcium oxide to form a system in which the glycol is insoluble. U.S. Pat. No. 5,552,023 S. J. Zhou employs a reverse osmosis membrane to achieve a first level of water removal followed by membrane evaporation employing a porous hydrophobic membrane.
Nevertheless, there remains a need for a heat efficient system for recovering the glycol of spent aircraft deicing fluid at a concentration acceptable for re-use of the glycol in an aircraft deicing fluid.